In the papermaking industry and the personal care field, it is common practice and well known to fiberize various cellulosic feedstocks for a variety of purposes. For example, in manufacturing airlaid tissue products, it is necessary to first reduce pulp sheets to individual fibers prior to depositing the fibers onto a forming wire. In the infant care and feminine care areas, pulp sheets are fiberized for making fluff for diapers and feminine products.
Many different types of apparatus are available for these purposes which can generally be classified into two categories, namely fiberizers and formers. Fiberizers, such as hammermills, serve to fiberize crude feedstocks, such as pulp sheets and waste paper, breaking down these feedstocks into a loose fibrous mass and individual fibers. On the other hand, formers are generally fed individual fibers or loosely bound fiber batts produced by a fiberizer and serve to lay the fibers evenly on a forming wire. There may be some overlap in the function of any given apparatus in that formers may accomplish some fiberization and fiberizers may be used to lay down fibrous batts. But all the different types of apparatus used for processing fibers share the common function of expelling individual fibers through an outlet while preferably retaining any clumps, nits, pills, or the like within the apparatus until they are sufficiently broken down or expelled through a separate recycle orifice. This is accomplished within a chamber enclosing arcuately travelling impact elements, such as blades or hammers, which thrust the fibers or fibrous material against the inner surface of the chamber. A portion of this inner surface contains an outlet having a large number of orifices through which small particles and individual fibers pass as the product of the apparatus. In the case of fiberizers and some formers, these orifices generally consist of holes drilled through the wall of the inner surface. In other formers, these orifices can also be mesh openings in a screen.
A problem which inevitably occurs with all prior apparatus of this type is that the outlet orifices become plugged with fibers at some level of throughout capacity, i.e. the throughput of the apparatus can be increased only so far, at which point it becomes plugged. Oftentimes this capacity limit is reached at an unacceptably low level of throughput. The apparatus illustrated in U.S. Ser. No. 4,375,447 to Chung and U.S. Pat. No. 4,375,448 to Appel et al utilize a slotted screen to overcome these problems, but the use of a woven screen still presents plugging problems, even if the screen openings are elongated rather than square.
Therefore, there exists a need for an apparatus for processing fibers which minimizes or inhibits plugging of the outlet orifices and therefore is capable of higher throughput capacity.